Modern audio frequency amplifiers provide flat frequency response over the whole audio range from 16 Hz to 20 kHz. To get faithful reproduction of sound we need depth of sound, which is provided by bass (low notes). Hence low-frequency notes should be amplified more than the high frequency notes (treble). To cater to the individual taste, and also to offset the effect of noise present with the signal, provision of bass and treble controls is made. The combined control is referred to as tone control.

The circuit for bass and treble control shown in the figure is quite simple and cost-effective. This circuit is designed to be adopted for any stereo system. Here, the power supply is 12-volt DC, which may be tapped from the power supply of stereo system itself. For the sake of clarity, the figure here shows only one channel (the circuit for the other channel being identical). The input for the circuit is taken from the output of preamplifier stage for the left as well as right channel of the stereo system.

Potentiometer VR1 (10-kilo-ohm) in series with capacitor C4 forms the treble control. When the slider of potentiometer VR1 is at the lower end, minimum treble signal develops across the load. The lowest point is referred to as treble cut. As the slider is moved upward, more and more treble signal is picked up. The highest point is referred to as treble boost. Bass would be cut if capacitive reactance in series with the signal increases. Thus, when the slider of potentiometer VR2 is at the upper end, capacitor C1 is shorted and the signal goes directly to the next stage, bypassing capacitor C1. Hence, bass has nil attenuation, and it is called bass boost.

When the slider is at the lowest end, capacitor C1 is effectively in parallel with potentiometer VR2. In this position, bass will have maximum attenuation, producing bass cut. Bass boost and bass cut are effective by ±15 dB at 16 Hz, compared to the out-put at 1 kHz. Treble boost and treble cut are also effective by the same amount at 20 kHz, compared to the value at 10 kHz.

After assembling the circuit, we may check the performance of the bass and treble sections as follows: